Search

This paper presents a research project proposal to ensure the optimum flow assurance for the development of heavy crudes, from offshore reservoirs to delivey points, considering several field facilities, which include optimum application and performance of chemicals to suppress or attenuate the precipitation of organic and inorganic deposits, corrosion inhibitors, as well as the treatment of emulsions produced due to the presence of formation water during production. The interaction between chemicals employed in well stimulation treatments and those used for crude dehydration is also considered.This proposal intends setting the basis to optimize flow assurance by minimizing the chemical dosage in the production and transportation facilities, maximizing the useful life of the employed chemical products. In order to achieve this goal it is necessary to include;– Laboratory studies to characterize heavy oil, water and gas properties and the interactions between the different fluids present, which allow evaluating the generation and stability of emulsions, hidrocarbons stability, and corrosion index of water, for example. – Evaluation of chemicals for flow assurance in the reservoir, lifting fluids in production wells, including artificial lift systems, as well as surface transportation and treatment fluids, and the interaction between these chemicals at different points during hydrocarbons production. – Generation of reservoir, well completion, wellbore and surface transport models.Pressure analyses show that production is dominated by high porosity vugs, and that the vertical permeability of vuggy areas is relevant for fields sharing an aquifer due to water channeling and the possible formation of emulsions inside the reservoir in the reion close to the producing wells.The assessement of the aforedmentioned issues can lead to the control and/or prevention of emulsion formation, solids deposition and corrosion. Besides, addressing each of these issues individually, it is important to assess the influence of a mixture of several chemicals at the bottomhole and surface facilities, providing useful information to anticipate and avoid additional complications derived from the application of several chemicals to address flow assurance problems from the reservoir to the delivery points.

In the Mexico marine region, gas breakthrough is common in naturally fractured carbonate oil reservoirs. Increasing the gas production reduces crude oil production, and eventually the wells become uneconomic and are shut-in in spite of the remaining recoverable reserves. A typical example is the Akal field, a large fractured 300-to 1000-m thick carbonate reservoir whose permeability varies between 0.3 and 5 darcy. The gas-oil contact zone moves by as much as 8 m/month as the natural gas and nitrogen gas from gas injection moves through the natural fractures and invades the oil zone. This condition results in production decline, reservoir pressure decrease, and oil remaining in the matrix. Efforts to selectively shutoff the gas have been unsuccessful due to the low-reservoir pressure and high-permeability contrast. When pumping water-based fluids, the increased hydrostatic pressure causes the treating fluid to travel down the natural fractures and away from the gas cap. This condition led to abandoning the gas-invaded intervals and recompleting lower in the reservoir, leaving some recoverable reserves. To selectively shutoff gas entry in fractured reservoirs, a stable foam-delayed crosslinked fluid was proposed for use by service company. The fluid with a high-foam quality (FQ) and low density rides over the crude and into the natural fractures/fissures, communicating with the gas cap. Once set, the fluid creates an impermeable seal with high-extrusion resistance. The stable foamed fluid has been successfully used to selectively shutoff unwanted gas production in wells that have been, in some cases, shut-in for several years due to excessively high gas/oil ratios (GOR). Following the treatment, the oil production was restored to the same level as prior to the gas breakthrough. The success of the initial campaign demonstrated that it is possible to restore the production levels of shut-in wells and recover otherwise lost reserves. This result has a very significant positive impact on the economics of operating the field. The current plan is to extend the use of the technique to other fields.